Long‐Term Exposure to Air Pollution and Incidence of Parkinson's Disease: A Danish Nationwide Administrative Cohort Study

Abstract Background Long‐term exposure to air pollution has been linked to Parkinson's disease (PD) incidence, yet evidence is mixed, partly because of challenges with PD diagnosis and definition. We examined this association in a nationwide administrative cohort. Methods We followed 3,280,190 Danish residents ≥30 years old from January 1, 2000 until December 31, 2018 for PD incidence, defined as either first hospital contact for primary PD or redeemed prescription of PD medication, as recorded in the Danish National Patient Registry or Prescription Registry, respectively. We assigned annual mean air pollution exposure concentrations at baseline residential address using the hybrid land‐use regression model (fine particulate matter [PM 2.5 ], nitrogen dioxide [NO 2 ], ozone [warm‐season, O 3 w], black carbon [BC]) rendered at 0.1 × 0.1 km. We used Cox proportional hazard models adjusting for age, sex, individual‐level, and area‐level socioeconomic factors. Results During a mean (standard deviation) follow‐up of 15.7 (5.6) years, 36,665 participants developed PD. Median (interquartile range [IQR]) exposure levels of PM 2.5 , NO 2 , O 3 w, and BC were 12.4 (2.0), 20.2 (7.9), 80.2 (4.3) μg/m 3 , and 1.01 (0.4) × 10 −5 /m, respectively. Hazard ratios (95% confidence intervals) for associations between air pollutants (per IQR) and PD incidence were: 1.05 (1.03, 1.07) for PM 2.5 ; 1.03 (1.01, 1.05) for NO 2 ; 0.98 (0.97, 1.00) for O 3 w; and 1.04 (1.02, 1.06) for BC. Conclusions In a representative nationwide cohort, we find that long‐term exposure to air pollution is associated with PD incidence. This unique study, with access to incidence data from administrative health registers, provides new evidence supporting air pollution as a PD risk factor. © 2026 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.